Are you sure? My understanding is/was that the sponsor is responsible for supporting the sponsored spouse/partner for 3 years, even if not reimbursing the government:
I think the way to look at this in terms of what's going on:
-yes, sponsor is responsible for 'basic needs';
-government can step in to provide something like/something government considers to be basic needs via social assistance (usually / mostly on a needs basis);
-government can, on basis of the sponsorship agreement, (attempt to) recover any funds paid to support the sponsored PRs;
-sponsors/spouses remain responsible for each other to whatever degree provided for under local/civil/contract means (i.e. prenuptial and other agreements, regular divorce/separation procedures, etc).
Put differently, the sponsor and sponsored spouse are responsible for each other the way any married/common law couple is - the one can sue the other. Government can't do much about that (xcept via the courts and etc, alimony and child support requirements to extent there are any). It's almost all a provincial matter.
The rest: govt doesn't make PRs (the sponsored ones) ineligible for social assistance - they still have access to the social safety net (however minimal). And a wee bit of stick in terms of the threat of recovery / ineligiblity for subsequent sponsorships.
They can attempt to check the sponsor has some minimal capacity to support a sposue but that's contingent on work, the market, health., etc - and willingness to actually do so. Or put differently, to some degree what government's doing is mostly about that last, the willingness - to ensure the sponsor has some incentive to not just abandon the spouse they sponsored.
Anyway 'why' it's like this is my interpretation, but I think in the main on the simple mechanics part it's accurate. If it helps anyway.
